Treatment of light hydrocarbons



TREATMENT OF LIGHT HY DRUCARBONS Warner E. Scovill, Lakewood, Ohio, assignor to" The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application January, 1952, Serial No. 267,913

8 Claims. (Cl. 196-30).

This invention relates to the treatment of low-boiling hydrocarbons. More particularly, the inventionrelates. to the treatment of liquefiedhydrocarbon gases, such as liquefied petroleum gases, oftenreferred to as LPG.

The light gasesandpartieularly the liquefied etroleum: gases have found wide industrial and commercial uses, as for example, combustion fuels and in. organic syn theses. These liquefied materials must for theirparticular uses comply with rather rigid" specifications on composition, vapor pressure, sulfur content. and corrosiveness. Typical of the: specifications'required for liquefied petroleum gas, for. example, are the following standards:

1. 03 on POD* analysis... min. 95%.by vol..

2. Vapor pressure 225 P. s.i.g. at105 F. max.

3. Contamination (Hg freeze 2% by vol.

max. test).

4. Non-volati1e material max. 0.5 cc./l. of materials 95 boiling'over 100 F. (no oily residue).

5. None.

7. Max. 15 grains/100 cu. ft.

8. Corrosiveness. Max. of 2. (Sohio Strip Test below) 40 9. Water None (per Go-Br Test).

*Podbielniaklow temperature fractional distillation equipmentsold by Porlbielniak, Inc., 341 EastOhio Street, Chicago 11, Illinois. This procedure and equipment is standardized throughout the industry.

One of the most serious problems in connection with these gases from petroleum sources is their corrosiveness which is generally the result of sulfur in some form and particularly free sulfur which may be inherently present in the gases or which may be formed by the decomposition of sulfureous compounds. Another form of corrosive sulfur which is frequently found in these gases is carbonyl sulfide (COS). Furthermore with the conditions to which the gases are subjected this compound may be decomposed into free sulfur. This decomposition may be accelerated by the presence of iron oxides in the form of rust or the presence of alumina in some of the subsequent treatment to which the gases are subjected.

It has been proposed to remove corrosive sulfur from light hydrocarbons by a number of methods including various absorbent materials which remove the sulfur compounds from the hydrocarbon stream, and various other materials usually in solution which react with the sulfur compounds to form sulfureous compounds which are more easily removed by either settling, filtration or sorption. In some instances the corrosive sulfur compounds are converted into a diiferent form which is less noxious and is left in the hydrocarbon stream. Carbonyl sulfides in particular have been removed by treatment of the contaminated hydrocarbons with basic cadmium or copper salts, and various amphoteric salts, inorganic sulfides, activated carbon, amines, and imines. However, none of these compoundsor methods has proved entirely satisfactory in removing the corrosiveness of some light hydrocarbon streams and a better method is still needed.

A satisfactory method for testing the corrosiveness of the liquefied petroleum gases has been developed which consists essentially of placing a clean polished copper strip /z" by 3" in a test bomb having a capacity of 6.75 cubic inches and containing 1 ml. of water and about 6 cubic inches of the liquefied petroleum gas to be tested.

Thebomb isimmersed in a 122" F. water bath for three hours; Thereafter, the stripis inspected for the degree of corrosion by. comparing it with standard reference strips which are numberedin the order of their increasing. discoloration as follows:

No discoloration.

orange to light yellow.

Yellow to pale grey.

Pale grey.

Gold.

Light Purple.

Purple.

Deep Purple.

Dark grey.

Black.

Black flakes.

A rating. of 2 or less on the above scaleis considered commercially acceptable.

I have found that the corrosiveness of liquefied petroleum gases may be materially reduced and in most instances completely eliminated to give a zero test on the above scale by treating the liquefied petroleum gases with lead or zinc mercaptides which may be conveniently impregnated on a carrier clay, such as fullers. earth, diatomaceous earth, Attapulgus clay, bauxite and similar relatively inert or inactive adsorbent and percolation carrier or other materials. The adsorbent carrier may be impregnated in any suitable manner with the mercaptide salts, such as by mechanically mixing the mercaptide salt into the clay or by forming the mercaptide salt directly in the presence of the clay. A convenient and preferred method of preparing a treating agent of the present invention consisting of lead mercaptide and clay is to charge Where R is an hydrocarbon radical preferably an alkyl group of 1 to 6 carbon atoms. The only limitation on the particular hydrocarbon mercaptan employed is the rate of the above reaction and the availability of the particular mercaptan. Ordinarily, the lighter aliphatic mercaptans, such as ethyl mercaptan, will be preferred, but butyl mercaptan has been used satisfactorily. The completion of the above reaction is indicated by the disappearance of the orange (PbO) color and the appearance of a yellow (lead mercaptide) color.

Zinc mercaptide impregnated clays can be prepared in a similar manner and can be used similarly as the lead mercaptides for satisfactory reduction of corrosive ness.

In the treatment of liquefied petroleum gases with the lead and zinc alkyl mercaptide-treating agents of the present invention, the liquefied petroleum gases are passed through the material at a rate of from 0.5 to 5.0 volumes of liquefied material per volume of treating agent per hour. However, other rates may be employed as long as there is suflicient contact time to obtain the desired improvement in the corrosive properties of the material treated.

Utilizing reacting agents prepared as described above in a series of tests, the following data are obtained. These tests were field runs under actual operating conditions where variables could not be controlled as: closely as in the laboratory. Those tests were selected where the conditions were sufficiently alike so as not to afiect the results significantly. The liquefied petroleum gas was treated at a temperature of 20 to F., depending upon the season of the year and whether the propane came from production or from storage. The temperatures within this Very faint discoloration. Light range do not affect the results significantly. The liquefied petroleum gas was passed through the treating agent at a rate of 1.1 to about 3.3 volumes of liquid per volume of agent per hour. The rate within this range does not affect the result significantly. The particular treating agent employed and the concentration of the mercaptide salts are indicated. The corrosion number based on the above scale is given for the liquefied petroleum gases before and after contact with the particular treating agent, as shown in the following table:

From the foregoing data, it may readily be seen that treatment of the light petroleum gases in liquefied form with the treating agents of the present invention materially and desirably reduces the corrosive properties of the liquefied products and brings them well within the commer'cially acceptable specifications for corrosiveness.

The above tests are to be compared with liquefied petroleum gas treated with clay alone and with clay modi fied by conventional agents, all of which treatments gave no substantial improvement or an improvement less than that necessary to meet the above-described test requirements.

The amount of the mercaptide on the clay is not critical. The mercaptide alone removes the corrosiveness but does not remain in an entirely desirable physical form because it tends to become crusted and consequently has a shorter life. Although the mercaptide may be used per se, it is preferable to employ it on the clay in an amount not to exceed 100% of the clay. The clay acts to retain the mercaptide mass porous and to prevent the dry mercaptide particles from agglomerating. When the amount of mercaptide on the clay is very small, a lower space velocity is required and a shorter life is to be expected. Clay with as little as 2 weight per cent of the mercaptide salts will remove practically all traces of corrosiveness of light petroleum products, even where the untreated material is unusually highly corrosive. In general, the most'desirable range, considering economic and other factors, is about 5 to preferably 25 to 50%.

The clay may contain agents other than the mercaptide, which are known for use with clay, and which do not affect the desirable results described, as claimed hereinafter. L

I claim:

1. A process for the treatment of a corrosive liquefied petroleum gas which comprises passing said liquefied petroleum gas in liquid state 'into contact with a bed of a mercaptide salt in a solid state of a metal from the group consisting of lead and zinc.

2. A process according to claim 1 in which said petroleum gas is a propane petroleum fraction.

3. A process according to claim 1 in which said mercaptide has 1 to 6 carbon atoms.

4. A process according to claim 3 in which said mercaptide is ethyl mercaptide.

5. A process for the treatment of a corrosive low-boiling hydrocarbon which comprises passing said hydrocarbon in liquid state through a bed of a solid material made by forming a mercaptide from the group consisting of lead and zinc mercaptides on an adsorbent carrier.

6. A process according to claim 5 in which said adsorbent carrier is a clay.

7. A process according to claim 6 in which said mercaptide is ethyl mercaptide and the metal is lead and is present on the clay in an amount of about 5 to 20%.

8. A process according to claim 5 in which the low boiling hydrocarbon is a liquefied petroleum gas.

References Cited in the file of this patent UNITED STATES PATENTS 1,718,713 Simpson June 25, 1929 2,055,423 Belchetz Sept. 22, 1936' 2,190,007 Batcheler et al Feb. 13, 1940 2,362,669 Schulze Nov. 14, 1944 

1. A PROCESS FOR THE TREATMENT OF A CORROSIVE LIQUEFIED PETROLEUM GAS WHICH COMPRISES PASSING SAID LIQUEFIED PETROLCUM GAS IN LIQUID STATE INTO CONTACT WITH A BED OF A MERCAPTIDE SALT IN A SOLID STATE OF A METAL FROM THE GROUP CONSISTING OF LEAD AND ZINC. 